1. Field of the Invention
This invention relates to novel mercapto group-containing silicone rubber compositions.
2. Description of the Prior Art
For purposes of the crosslinking and curing of silicone rubbers, there have been proposed a method in which an organic peroxide is incorporated as a curing agent in a diorganopolysiloxane, the main raw material, and a method in which a platinum compound as a catalyst for addition reaction and an organohydrogenpolysiloxane as a crosslinking agent are incorporated in a vinyl group-containing, high-molecular-weight diorganopolysiloxane. According to these conventional methods, however, it is difficult to satisfactorily cure the silicone composition in which a strong reducing agent is included. Further, according to the conventional methods, the curing of the silicone rubber is insufficient at the areas where the silicone rubber is contacted with a substance having reducing activities or a material containing a reducing agent, or with an organic synthetic rubber of the sulfur vulcanization type, since the synthetic rubber usually contains a sulfur compound, antioxidant, or aging-retarder. Further, the carbon black as a most widely used filler in the organic rubbers may affect the curing of the silicone rubber very badly when the latter is in contact with the former.
With recent development of silicone rubbers, it has become required to prepare laminations of a silicone rubber and an organic synthetic rubber by simultaneous vulcanization and further, for the purpose, to develop new crosslinking and curing methods in a convenient and effective manner.
On the other hand, when the silicone rubber composition to be cured contains unsaturated groups, for example, vinyl groups, of the organopolysiloxane in an amount not lower than 10 mole % based on the total organic groups (for example, the amount is in general between 0.1 and 1 mole %), sulfur-vulcanization is possible. However, the resultant sulfur-vulcanized silicone rubbers having a substantial content of vinyl groups tend to have very poor physical properties, particularly mechanical strengths, and those products can hardly be put to practical use.